116 STUDIES IN IMMUNITY. 



When streptococci have remained for several hours in the pro- 

 toplasm of the phagocyte some of them take acid dyes in preference 

 to basic dyes; in a counter stain with eosin and methylene blue 

 such bacteria take a more or less red stain. This phenomenon 

 occurs both in the rabbit and in the guinea-pig, but in the latter is 

 more evident on account of the greater extent of the phagocytosis. 



II. 

 ANTISTREPTOCOCCUS SERUM. 



Marmorek, in an article published in July, 1895, in the Pasteur 

 Annals, has described his method of obtaining this serum by im- 

 munizing animals against the streptococcus. 



We shall not reiterate his methods. It may be noted simply that 

 the serum we have used was from animals that had been under 

 immunization for about a year. One of these, the serum of which 

 was remarkably active, had received twenty- three injections of 

 a very virulent 24-hour culture. The total amount of culture 

 injected during this time was 3800 c.c. 



The preventive activity of these sera is most evident. When 

 injected into a rabbit before inoculation of bacteria, they permit the 

 animal to withstand many times the minimal fatal dose of strepto- 

 coccus. 



The amount of bacteria that can be safely injected in animals 

 immunized by serum varies a great deal according to the region 

 in which the injection is given. Animals that have received 

 serum do not tolerate intraperitoneal injections of streptococci 

 nearly as well as they do subcutaneous injections. Intravenous or 

 intraocular injections are also much more dangerous, even in 

 animals that have received a very highly active serum. In deter- 

 mining the preventive value of a given serum the portal of entry 

 chosen for inoculation of the culture should therefore be indicated. 

 For this reason we shall frequently mention the doses of serum and 

 culture used in our experiments. 



A few figures from our notebook may be given at once as show- 

 ing the result of injecting a culture subcutaneously in passively 

 immunized animals. 



An animal that has received 10 c.c. of serum subcutaneously can 



